Gst transition benefit

Polyester SEWING thread falls in HSN code 5508 is chargeable 18% GST. At present we pay excise on Polyester fibre and dyes/ chemicals @ 12.5%. Sewing thread at present is charged at nil rate of duty in excise with the condition that we do not take input Credit of excise paid on Fibre and Dyes etc. We have given declaration to this effect and as such are exempted from taking Excise Registration. PL ADVISE whether we will get input Credit of excise duty paid on raw material and finished goods lying in our factory. And at branches where it is sent against F form at the time of transition. We are also consignment agent of another company who sells zippers. the stocks of these zippers are also lying at our branches for which we have 12.5% excise paid bills sent to us against form F without charging Vat/CST. What treatment should we do for the zippers. Please advise on the above.. Warm Regards J D Marwah 9811667702